The Social Brain Flashcards
(44 cards)
Brain size
Body weight increases quicker than brain weight (Roth & Dicke, 2005).
- brains of hominoids evolved faster than apes.
- homosapiens have largest relative brain size.
Special case primates:
- evolvement of large brains happened to all vertebrate taxa.
- but social brain hypothesis different in other mammals and birds.
- eg. bird brain size related to pair bonding.
Humans/primates = related to stable relationships and social network size (Shultze & Dunbar, 2007).
- possibly due to cognitive demands of sociality placing a constraint on number of people that can be maintained in a coherent group (Dunbar, 2009).
Evolvement of the neocortex: (NC + allocortex = cerebral cortex)
Neocortex = largest and outer part of the cerebral cortex covering two hemispheres.
- responsible for higher functions.
Allocortex = smaller, mainly olfactory system and hippocampus.
Evolvement of the neocortex: neocortex
Evolution of the brain:
- reptilian brain -> mammalian brain -> neocortex.
- breathing/hunger/temperature -> memory/love/anxiety/sociality/fear -> logic/language/morality/emotional control etc.
Functions: survival -> adaptation to environment -> high functions.
Neocortex is necessary for high social functions - our most powerful “tool”.
Evolvement of the neocortex: cost of a large brain
Brain responsible for 22% resting energy expenditure (McClave & Snider, 2001).
- 2/3 of neural firing; 1/3 for maintenance.
- some say that liver costs more.
Evolvement of the neocortex: evolution of the neocortex
Needs large brain to support it.
Large brain demands sufficient energy supply (nutritious diet).
- some argue that the use of fire improved nutrition intake and is a key factor in human evolution.
Social brain can benefit the species and offset extra energy demand (Dunbar & Shultz, 2007).
Social brain hypothesis
Proposed by Dunbar - argues human intelligence did not evolve primarily as a means of ecological problems, but instead as a means of survival and reproducing in large social groups.
Brain and social networks: neocortex in primates
Neocortex: accounts for most of the differences between living primate taxa (Stephan, 1972; Passingham, 1982).
Sociality: Our evolutionary goal.
Brain and social networks: neocortex ratio (in comparison to rest of brain)
Neocortex ratio (CR) = NC volume / (brain volume - NC volume)
In humans NC volume = 1006.5cc.
Total brain volume = 1251.8cc (Stephen et al, 1981).
About 50% larger than the max value for any other primate species (Dunbar, 1992).
Brain and social networks: ecological or social?
Primates have larger brains because:
Ecological theory (eg. Gibson, 1986) - large brains provide ecological functions of cognitive skills.
- especially in large ecologically flexible species like primates.
(OR)
Social theory (eg. Byrne & Whiten, 1988) - large brains mainly for social function to intellect, emphasising uniquely complex nature of primate social life.
Brain and social networks: Dunbar’s work
Data on neocortex volume, group size and other behavioural ecology variables (body mass, fruit in diet, activity etc) collected from 38 primate taxa correlated (Dunbar, 1992).
- group size positively correlated with CR - SUPPORTING SOCIAL INTELLECT THEORY.
- number of relationships able to monitor simultaneously is limited by size of neocortex.
- group over this limit is unstable.
Brain and social networks: grooming is a social activity
Social animals adapt grooming behaviours to bond and strengthen social structures.
Plays important role in forming social bonds in many primate species.
Brain and social networks: social network size
In primates large groups are created by welding together sets of smaller grooming cliques (Dunbar, 1992).
- clique sizes correlated significantly with CR in primates (Kudo & Dunbar, 2001).
Brain and social networks: Dunbar’s number
CR vs group size (Dunbar, 1992; 2003)
- steeper increase in apes than monkeys.
Dunbar extrapolated the correlation and suggested a number of 148 for effective human social group size.
- rounded to 150 = Dunbar’s number.
- 231 = Bernard-Killiworth’s number (1987) - not as popular.
Brain and social networks: social groups
Predicted social group size for hominoid populations using regression.
Group size increased during primate evolution (Dunbar, 2003).
Brain and social networks: interpreting Dunbar’s number
“Number of people you wouldn’t mind joining uninvited if you bumped into them” - Dunbar, 1998.
Social brain hypothesis often formulated in terms of this number.
But is more correct to think of as a measure of complexity of social relationships.
Relationships need maintenance, consuming energy and time, thus require a more developed brain.
Social networks in humans: human society
Dunbar’s number is an estimation - needs to be checked.
Social networks in humans: using Dunbar’s number
W.L Gore & Associates - buildings accommodate 150 employees.
Swedish tax authority - organised offices max 150 per office.
Any group greater than 150 - becomes dysfunctional.
- company size = 75-200.
- organisations > 150 need bureaucracy.
Social networks in humans: social group layers
Support clique: people we seek personal advice from.
Sympathy group: special ties, frequent contact.
Band: acquaintances, less frequent.
Clan: all current contacts.
Megaband & tribe: larger social units.
Closeness and mean time spent interacting with individuals decreases in each layer as the number in the social group increases (Sutcliffe et al, 2012)
Social networks in humans: the expanding circles
Our relationships form a hierarchically inclusive series of increasing size but decreasing intensity (i.e. quality of relationship).
- 150 = limited reciprocated relationships.
- 1500 = limit on memory for faces?
Each circle is 3X larger than the one inside of it (Dunbar, 2014; Roberts, 2010).
Social networks in humans: social media
Can we have a larger network online? - no.
With online group size similar to f-to-f networks (Dunbar, 2012;2016).
Relationship quality suffers without f-to-f interaction.
Similar results found for mobile phone networks (Miritello et al, 2013).
Social time: Mind the gap: why is it important?
Grooming as the bonding agent in primates.
- grooming time determined by group size.
- upper limit about 20% of total daytime.
Social time: social grooming in humans
Humans version = conversation.
Mechanism of social bonding: 60% of conversation is to social topics (eg. gossiping; Dunbar, 1993/2004).
Similar to primates - social grooming.
Language evolvement = gossiping.
Social time: bridging the gap
Religion and its rituals.
Music and dance.
Laughter - trait shared with chimps.
Social time: how grooming works
Music and laughter triggers endorphin uptake (Dunbar, 2012a;b).
- endorphins are relaxing.
Create psycho-pharmacological environment for building trust?
